This invention is to provide a heating furnace having such means which can adjustably control a flow of gas atmosphere within the furnace. More specifically, this invention is to provide, to a continuous gas atmosphere heating furnace consisting of a preheating chamber, a chamber for heat treatment such as brazing, and a cooling chamber, with means for adjustably controlling a flow direction and amount of an atmosphere gas which has been applied into the furnace and is circulated within one or both of the preheating and cooling chambers by fan means in a direction transverse to and substantially at a right angle with the longitudinal axis of the furnace so as to be repeatedly in contact with heating or cooling means in the chambers, heated or cooled thereby, and in contact efficiently with articles under the heat treatment.
A continuous gas atmosphere heating furnace of the kind mentioned above and as illustrated in FIG. 1 which shows as an example of this invention a heating furnace for brazing aluminum articles, employs a gas atmosphere of N.sub.2 gas and so on of a high purity for the prevention of oxidation of aluminum articles and brazing materials applied thereto. In order to keep the purity of such gas atmosphere, the furnace employs a metallic muffle case, or inner walls of the furnace which are made from refractory materials, are lined with metals. In case of the furnace utilizing a muffle, the heating of a gas atmosphere and consequently of articles passing through said gas atmosphere is made indirectly by heating means which are located outside the muffle (the heating means could be bare in this instance). And, in case of the furnace, refractory inner walls of which are lined with metals, heating means such as a pipe heater which is not bare, has to be used. At any rate, the heating of articles to be treated depends primarily on radiation transmission of heat. Under such heating, however, it takes much time until the articles such as aluminum products having bright surfaces are heated to a desired temperature, because their surfaces has extremely low emissivity. When it takes much time to heat articles to a predetermined temperature, and consequently when the articles stay within a furnace gas atmosphere for a comparatively long period of time, outer surfaces of aluminum articles and brazing alloys applied thereupon tend to be oxidized even by a very trace amount of O.sub.2 and H.sub. 2 O contained in the furnace gas atmosphere such as N.sub.2 gas. Oxidation of the articles at their surfaces most adversely affects brazing thereof.
Under the circumstances, it is required, therefore, to heat the articles rapidly. And, in order to achieve this end, it has been proposed to heat the articles in a preheating chamber into which they are first introduced, not only by the aforementioned radiation transmission of heat but also by forced heat convection, medium of which is the furnace gas atmosphere such as N.sub.2 gas. This kind of forced heat convection is produced in the preheating chamber by circulation fans provided at an elevated position in the chamber. In this instance, the gas atmosphere in the preheating chamber is circulated along planes in transverse and vertical to a longitudinal axis of the furnace or forwarding direction of articles within the furnace, and repeatedly makes contact with heating means which are provided outside a moving path of the articles, to be heated by the heating means and to heat the articles in turn. The gas atmosphere thus circulated along the above-mentioned vertical planes in the chamber does work, on one hand, as if it were pneumatic curtains extending transversely to the furnace. To wit, such vertically extending curtains of circulation gas bar the free flow of furnace gas atmosphere which slowly streams from a gas inlet to an intake opening of the furnace via heat-treatment and preheating chambers, and from the gas inlet to an outtake opening for articles via a cooling chamber. Since the gas atmosphere which has been introduced first to the heat-treatment chamber, heated and expanded therein, tends to be a kind of resistance against the above-mentioned free flow of furnace gas atmosphere, the vertical curtain-like circulation of gas further retards said free flow. This has to be avoided really. Retardation of the flow of atmosphere gas within the furnace chambers though it is slow, lowers high purity of the gas as it is not continuously refreshed. It shall be noted also that when the gas flows too much in a single direction, viz., toward the cooling chamber, being barred in the heating and/or preheating chambers, air is sucked from the other direction, viz., into the preheating chamber, whereby the atmosphere gas becomes impure.